1. Field of the Invention
The present invention relates to a control method for controlling fan speed for the thermal fan unit. In particular, it is relating to a fan speed control method, under several power supplies for mobile electronic devices, capable of improving the heat dissipation capability for a mobile electronic device or extending battery life at the same time.
2. Description of the Related Art
Because of recent trends in electronic device miniaturization, electronic device functionality has become more advanced, the internal temperature of electronic device has become higher and higher. In addition, the trend is towards higher power consumption; therefore, ability to obtaining an improved thermal management environment and, at the same time, capability for extending battery life are important objectives for mobile electronic devices.
In mobile electronic devices, a fan is typically the primary element which is relied upon for providing the primary thermal management function, releasing of thermal energy from the inside of mobile electronic devices or suction for outside cooler air to enter inside, and preventing device internal elements from overheating, which leads to excessive thermal and performance degradations. Mobile electronic devices include notebook computer and desktop computer. Conventional method for fan control is done using a fan control table and fan speed for controlling the internal temperature of the mobile device. One of the temperatures chosen for temperature control is the processor temperature. Because the processor is a component that releases the most thermal energy in the device and because of excessive temperature leading to degradation of components, the fan is used to provide the thermal management function for the processor.
To prevent excessive acoustic noise from extended running of the fan at excessive speeds, the fan typically adjusts its fan speed, raising or lowering the speed corresponding to the processor temperature for providing adequate thermal management capability and for preventing excessive acoustic noise causing user discomfort. However, by using only the fan control table derived from the processor temperature and the fan speed for fan control, it leads to severe battery drain while the mobile electronic device is operating in battery mode because of the added power consumption requirements directly relating to unnecessary heat dissipation. While the mobile electronic device is using its battery mode for power source, the processor frequency is automatically lowered to prevent excessive thermal buildup. At this time, the continuing use of the fan control table obtained from corresponding fan speed with respect to the original processor temperature leads to excessive heat dissipation and reduction in power availability, which leads to an increase of acoustic noise given off by the fan.
Referring to FIG. 1, it is a schematic diagram for a conventional fan speed control technology, taken from Taiwan Patent Application No. 093124620 entitled “Automatic Fan Micro-Adjustment Method”, filed Aug. 17, 2004, owned by the same assignee. The conventional technology is using a fan control table, derived from the fan speed relation with respect to a single temperature reading, to stabilize the fan's thermal management system and to manage the accompanying acoustic noise. As soon as the processor temperature is raised, while the fan speed is below the fan control table's indicated benchmark value, the fan speed gradually increases to raise the processor's heat dissipation capability and to prevent excessive acoustic noise (step 620). As soon as the processor temperature is lowered just as the fan speed is above the fan control table's indicated benchmark value, the fan speed gradually decreases to reduce power consumption (step 626). Using conventional technology to control fan speed can only achieve limited power consumption savings, for it is only using the fan control table obtained from only one temperature reading with respect to fan speed and it is suffering from excessive drain on the battery power.